Chapter_One_PPT_Voice_Before_Convergence.pdf

7/29/2019 Chapter_One_PPT_Voice_Before_Convergence.pdf

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Chapter 1

Perspectives on Voice BeforeConvergence


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Overview (reference chapter 1)

Describe the simplest type of modern voice communication

Describe the process of converting analog voice into digital signals

Describe the process of using digital to send multiple calls over a single line

Describe the components of the PSTN

Compare PBX and Key systems and methods to connect to the PSTN

Describe numbering plans


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Analog Connections Your voice is converted into electrical signals

Analog phones use those electrical signals toconvey changes over the cable

Different types of signals are also conveyed Dial-tone, digits dialed, busy signal ect.


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Loop Start and Ground SignalingWhen the phone is on-hook, the phone

separates the tip and ring.


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Loop Start and Ground SignalingWhen the phone is lifted off-hook, the

phone connects the two wires, causing

48V DC to flow from the phone company

central office into the phone.

Loop start is susceptible to GLARE

GLARE occurs when you pick up the

phone to make an outgoing call at the

same time an incoming call.


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Loop Start and Ground Signaling GLARE is not a problem in home environments.

GLARE will effect business using a key system with multiple

lines. Modern PBX systems use ground start signaling to alleviate

GLARE

From the PBX side, the RING lead is grounded first, then the

central office circuit must ground the TIP lead before the PBXcan close the loop between TIP and RING.


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Signaling Types There are three types of signaling used in a telephony network:

Supervisory signaling communicates the state of a telephony device.

Address signaling sends information about the digits dialed.

Informational signaling communicates the current state of the call.

Signaling can be sent either in-band or out-of-band

In-band signaling sends the signaling in the same communications channel as

the voice.

Out-of-band signaling sends the signaling in a separate communications

channel from the voice.


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Supervisory Signaling


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Informational Signaling Example


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Address Signaling


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Analog Signal Repeaters

Repeaters regenerate signals including noise


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Digitizing Analog signals

Sample the analog signal regularly.

Quantize the signal. Encode the value into a binary expression.

Compress the samples to reduce bandwidth

(optional)


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Sample the Signal


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Quantize the Signal


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Encode the Signal in Binary


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Sending Multiple Calls over a Single

Line


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T1 Circuits

Up to 24 channels for voice

Each channel Digital Signal 0 (DS0)

Every 6th frame is used for signaling information

24th DS0 has an extra bit used for framing

Each DS0 is 64 kb/s

8000 samples per second

One byte per sample

One sample per channel, per frame

Super Frame (SF) groups together 12 frames

Extended Super Frame (ESF) groups together 24 frames


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CAS T1 Signaling BitsIn-band


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Channel Associated Signaling (CAS)


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Common Channel Signaling Allows multiple services through one line. Well adapted for voice.

64 kb/s B channels

Q.931 protocol used on the D channel

Supports proprietary signaling on the D channel.

Used internationally.

Out-of-band


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Public Switched Telephony Network


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Traditional Business Phone Systems


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Key System


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PSTN Numbering Plans A numbering plan is a numbering scheme with the following

characteristics:

Defines a set of rules to allocate numbers used in telecommunications

Is based on international telecommunications standards Is established by numbering plan authorities, which regulate the distribution of numbers

and codes in their territory

Many regional and national numbering plans exist:

North American Numbering Plan (NANP)

U.K. National Numbering Scheme

European Telephony Numbering Space (ETNS)

Hong Kong

Many countries have their own numbering plans


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North American Numbering Plan NANP is the numbering plan for the United States and its territories,Canada, Bermuda, and many Caribbean nations.

Administered by the NANPA

NANP numbers are 10-digit numbers.


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NANP Numbering Plans 456-NXX-XXX codes Carrier ID for inbound international calls

NXX defines the carrier

555-01XX line numbers Reserved for fictitious use

800-XXXX through 855-XXXX line numbers

Reserved for the deaf, hard of hearing, or speech impaired

900-NXX-XXXX codes Premium services billed to calling party

Service provider ID is imbedded in the NXX code


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E.164 Addressing

E.164 is an international numbering plan for public telephony

systems:

A valid number contains the following components:

Country code

National destination code (area code and exchange in North America)

Subscriber number

Each number can be up to 15 digits long

The E.164 plan was developed by the ITU


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Summary Wired connections to an analog phone

Supervisory signal types

Informational signal types

Address signaling types

Time division multiplexing

Deliver signaling with digital

Components of PSTN

Chapter_One_PPT_Voice_Before_Convergence.pdf

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